I have two smoke alarms in my flat. Recently I had to change the battery for one of them, so I switched off the mains, disconnected the alarm, replaced the battery, tested it, and reconnected the alarm. However, upon switching the mains back on, both alarms started beeping.

Even if I physically remove either one of the alarms, the other will beep. I'm aware that smoke alarms are daisy chained so that when one alarm is activated all the other alarms will sound an alert, but if one is removed from the system, does that normally automatically activate the remaining ones?

Also, both work normally when I push their test buttons. Anyone have any idea what's happening/how to fix it?

  • Hello, and welcome to Stack Exchange. What manufacturer/model are your alarms? – Daniel Griscom Aug 20 '16 at 14:22
  • Hi! The first is a BRK 670MBX "SD3-plus ionization type smoke alarm", and the second is a BRK 690MBX mains powered heat alarm. Links to their specs are below. Thanks! screwfix.com/p/… screwfix.com/p/… – 3lbom Aug 20 '16 at 14:28
  • Do they beep one time when power is switched on, or as "start beeping" would imply do they continue to beep? If they continue what interval do they beep? How do you stop it? turn them back off? – Tyson Aug 20 '16 at 16:19
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    Ours beep if the battery door is closed but with no battery or a flat battery. You may find that you should apply the mains without the battery in, then fit the battery. Obviously not if you have to open it right up to change the battery and so expose the mains. And check the manual if you have it. – Chris H Aug 20 '16 at 16:46
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    I have had trouble with mains connected detectors after doing remodels. What I found out was the dust caused the ionizing chamber to alert. You may have a similar problem. – Ed Beal Aug 20 '16 at 21:54

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